The instant invention relates to a device for laying yarn on a cross-wound bobbin.
Yarn guidance rods made of high-strength plastics are known from DE 33 45 743 A1, but according to this disclosure their surfaces are not entirely plane, this being caused by manufacturing conditions. For this reason, difficulties arise in the axial guidance of the yarn guidance rod. It is therefore proposed in the DE 3345743 AL to use roller guiding elements to support the yarn guidance rod for axial guidance. With this type of mounting, however, it is a disadvantage that the yarn guidance rod which is moved back and forth at very high speed and may be over 30 meters long, must accelerate the mass of the roller guidance elements in addition to its own mass. The savings in mass which is obtained on the one hand by using plastics is cancelled out again on the other hand due to the weight of the roller guidance elements to be accelerated.
DE 3434027 A1 proposes a plain bearing to support the yarn guidance rod. To avoid disadvantages due to the uneven surface of the extruded profile, bearing elements which interact with bearing elements mounted on the machine are mounted on this yarn guidance rod. This device has again the disadvantage that additional components must be accelerated.
This DE 3434027 A1 reference furthermore discloses yarn guidance rods consisting of extruded profiles containing fibers reinforced with artificial resins, carbon fibers among others. These carbon fiber-reinforced rods possess a high degree of static and dynamic strength and little heat expansion. The heat expansion is especially very low when the fibers are oriented in stretched form in the longitudinal direction in the fiber guidance rod. This low degree of heat expansion is produced in a disadvantageous manner in that heat expansion is very different for the yarn guidance rod as compared to the machine frame which is normally made of steel. This difference in heat expansion causes a lateral offset in winding the yarn on the cross-wound bobbin, especially when starting up a cold machine until it reaches its heated state. In extreme situations the yarn falls off from the bobbin on the side as it is wound up and prevents orderly build-up of the bobbin.
Yarn guidance rods with fibers in the longitudinal direction of the yarn guidance rod also have the disadvantage that the required transversal strength, i.e the strength concerning forces in the radial direction in relation to the cross-section of the yarn guidance rod, is no longer sufficient, especially at high traversing speeds and with long yarn guidance rods. The rods must therefore have a very large cross-section, as they otherwise cannot withstand the extreme loads.